TDI%p: 100p% of the paired reading ratios are within 1/(1+TDI%p) and 1+TDI%p. For example, TDI%0.9=10% means that 90% of the ratios of the paired readings are within 1/1.1 and 1.1. It also means that 90% of the paired readings do not deviate more than 10% from each other. This is also the 90% quantile of individual percent changes. This index would be evaluated using a testing criterion, such as the Proficient Testing Criterion (PTC), which is measured by percent change.
TDIp: 100p% of the absolute difference of the paired readings are within TDIp. For example, TDI0.95=10 means 95% of the absolute difference of the paired readings are within 10 units, or 95% of the paired readings do not deviate more than 10 units from each other. This is also the 95% quantile of individual absolute differences. This index will be evaluated using a testing criterion based on absolute difference.
CPPTC or CPPTC%: Coverage probability (CP) gives the probability of observations within PTC unit or PTC% of the target values. For example, CP20%=0.93 means that 93% of the readings are within 20% difference of the target values. For CP5=0.97, it means that 97% of the readings are within 5 absolute differences of the target values.
Accuracy Coefficient: Ca measures the closeness of the observations and target values in terms of both mean and variance. There is no difference in mean and variance between test and reference devices when Ca=1 (i.e., the method has perfect accuracy).
Precision Coefficient: Pearson correlation coefficient (r) measures how closely the observations deviate from the best-fit line.
CCC: Concordance Correlation Coefficient (CCC) measures agreement between observations and target values or measures agreement of observations against the identity line. It is the product of accuracy and precision coefficients (CCC=rCa). CCC=1 stands for perfect agreement (all observations=target values). CCC=0 stands for no agreement. CCC=-1 stands for perfect reverse agreement. When we evaluate agreement among paired readings across all data range, we should expect CCC>0.99.